BD9285F Datasheet, PDF (9/39 Pages) Rohm – Boost 1channel white LED driver For large LCDs

BD9285F
Datasheet
●2.4 Pin function description
○Pin1: OVP
The OVP terminal is the input for over-voltage protection and short circuit protection of output voltage. As OVP is more
than 3.0V, the over-voltage protection (OVP) will work. On the other hand, OVP is lower than 0.2V, the short circuit
protection (SCP) will work. At the moment of these detections, the BD9285 stops the switching of the output GATE and
starts to count up the abnormal interval, but IC doesn't reach latch off state instantaneously until the detection continues
up to the number of counts of GATE terminals, which depend on the kind of abnormality. (Please refer to the time chart in
the section 3.5.7)
The OVP pin is high impedance, because the internal resistance to a certain bias is not connected.
So, the bias by the external components is required, even if OVP function is not used, because the open connection of
this pin is not fixed the potential.
The setting examples is separately described in the section 3.4.6, ”external components selection, how to set OVP, SCP”
○Pin2: UVLO
Under voltage lock out pin for the input voltage of the power stage. More than 3.0V(typ.), IC starts the boost operation and
stops lower than 2.8V(typ.).
The UVLO pin is high impedance, because the internal resistance to a certain bias is not connected.
So, the bias by the external components is required, even if UVLO function is not used, because the open connection of
this pin is not fixed the potential.
The setting examples is separately described in the section 3.4.5, ”external components selection, how to set UVLO”
○Pin3: SS
The pin which sets soft start interval of DC/DC converter. It performs the constant current charge of 3.0 µA to external
capacitance Css(0.001µF to 4.7µF). The switching duty of GATE output will be limited during 0V to 3.0V of the SS
voltage.
So the equality of the soft start interval can be expressed as following
Tss = 1.0*10⁶*Css
Css: the external capacitance of the SS pin.
Regarding of the logic of SS=L
(SS=L) = (PWM1andPWM2 have not asserted H since ResetB=L->H) or (latch off state)
where ResetB = (STB=H) and (VCCUVLO=H) and (UVLO=H) and (TC54UVLO=H)
Please refer to the time chart on soft start behavior in the section 3.7.4
○Pin4: RT
DC/DC switching frequency setting pin. RT set the oscillation frequency inside IC.
○The relationship between the frequency and RT resistance value (ideal)
R _RT
=
15000
f _SW [kHz ]
[kΩ]　
The oscillation setting range from 50kHz to 800kHz.
The setting examples is separately described in the section 3.4.4, ”external components selection, how to set DCDC
oscillation frequency”
○Pin5, Pin6: PWM1, PWM2
The ON / OFF terminal of the LED driver. LED lights when both PWM signal are high (DIMOUT = H). The Duty signal of
this pin can control the PWM dimming.
The high / low level of PWM pins are following.
State
PWM1=H or PWM2=H
PWM1=L or PWM2=L
PWM input voltage
PWM=2.0V to 5.0V
PWM=‐0.3V to 0.8V
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TSZ22111・15・001
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TSZ02201-0F1F0C100030-1-2
11.Jul.2012 Rev.001